1. Field of the Invention
This invention relates to centrifugal separators for the separation of particles or drops of a denser material from a liquid or gaseous carrier medium to be cleansed, especially for the separation of liquid drops from a gas, particularly air or natural gas.
More particularly the invention involves a separator device wherein a stream of the medium to be cleansed is introduced through at least one entrance aperture of the device, such device including means which is provided for the purpose of regulating the volume of the introduced stream.
The invention relates further, in a general sense, to a device for the separation of particles or drops of a denser material from a gas to be cleansed, and in more detail for the separation of dust as well as liquid drops of water and/or oil from compressed air or natural gas, with a solids filter interposed in the feed pipeline and with a centrifugal separator disposed downstream from the solids filter, for the separation of the liquid drops.
Finally, the invention relates to a method for setting the volume of the stream flowing through the centrifugal separator.
2. Description of the Related Art Including Information disclosed under 37 CFR .sctn..sctn.1.97-1.99
In many areas of technology it is necessary to clean a medium flowing through a pipeline, of various components of a contaminating medium. The medium to be cleaned can be liquid, but in the majority of applications it is gaseous. The invention is particularly well suited for devices in which a gaseous medium is to be cleaned, but it is not restricted to such devices. An example of the technical area in which the invention can be realized especially concerns the purification of a gas in pressure regulating stations whence the gas is fed into a distribution network. This includes, for example, pressure regulating stations in natural gas supply locations or compressed-air ductwork systems, where natural gas or compressed air is to be cleaned of dust and liquid components such as condensed water or oil.
According to the state of the art, there is provided in such stations, first of all, a solids filter in which are arranged e.g. candle-shaped filters by means of which the solid particles are removed from the gas passing through. The liquid vapors contained in the gas which condense out due to the pressure drop occurring above the filter, cannot be removed by the solids filter, however. Therefore, according to the state of the art, a centrifugal separator is provided downstream of the solids filter, which causes the gas to move essentially in a circular or spiral path that produces a sink. The sink represents a centrifugal field of force in which the liquid droplets which enter it together with the gas flow, also have a circumferential speed that, in a centrifugal separator of spiral construction, increases from the outside to the inside in accordance with the rule of twist.
Co-rotating particles experience a centrifugal force and push other particles outwardly. The centrifugal force is proportional to the mass of the particle, to the square of the circumferential speed and inversely proportional to the radius of the momentary circular motion. Countering the centrifugal force are forces of resistance, for which reason there is a radius where the centrifugal force equals the force of resistance.
A particle of a certain size or of a determinate floating velocity will then circle continuously, whereas bigger particles will move outwardly and become separated. It follows from the foregoing that in order to separate liquid drops as small as possible, high circumferential speeds must occur, and the inner radius of the centrifugal separator must be as small as possible. Expressed differently, it is desirable when separating liquids from gases, that the liquid droplets be as large as possible.
Therefore, the maxim is that a centrifugal separator of large dimensions is inferior to one having small dimensions with respect to the limiting size, i.e. the smallest liquid drop still separated. In the past, therefore, multicyclones have already become known, which are composed of individual centrifugal separators of smaller size. But in particular, wherever large quantities of a gas are to be cleaned they have been put through centrifugal separators of larger size as a matter of preference--in particular because of the lower manufacturing costs. Such larger-sized centrifugal separators pose problems whenever the volume stream which is to be put through varies greatly in band width, i.e. whenever a shut-off valve and regulating member or valve ahead of the entrance aperture of the separator restricts the volume flow. Particularly in the applications mentioned, i.e. when purifying natural gas or compressed air at pressure regulating stations, there will occur a problem because the flow turbulences caused by the shut-off valve result in the liquid droplets contained in the gas flow becoming atomized to the point where their diameter drops below the limit applicable to the centrifugal separator designed for maximum flow volume, meaning that such droplets will not be separated.
Besides the droplet size reduction of the liquid to be separated, as a consequence of atomization, it is a further disadvantage of the known arrangement, in which a shut-off member is disposed in a pipeline designed for maximum volume flow throughput, that the flow velocities in the pipeline are low in small throughputs, i.e. small volume flows. This also means that the entrance velocities of the gas flow into the centrifugal separator are slow as well and, accordingly, the circumferential speeds in the sink generated in the centrifugal separator are correspondingly slow so that, in addition to the negative influence that the liquid drops to be separated by atomization have been reduced in size, the unfavorable circumstance is added that the centripetal acceleration acting upon the respective drops and proportionately governing the generation of a centrifugal force becomes smaller. This latter circumstance is intensified in particular by the fact that the centripetal acceleration depends quadratically on the circumferential speed.
It can be stated in summary that centrifugal separators in the above described applications are being built, for design reasons and to keep investment costs low, for maximum throughput, but that, in the arrangement with a preceding shut-off member in the supply line as known from the state of the art, they work unsatisfactorily when set to low volume flow of the medium to be purified.
In DD 27 68 15 A the dependence of the separation output on the material throughput in cyclones is referred to. The insertion of flaps or the like changing the entry impulse of the material flow is said to be disadvantageous because an unfavorable intervention in the flow conditions is said to be connected with it. It is suggested that the entire material flow led to a swirler be divided before the swirler by a first division into two or more partial flows, of which at least one is led via a valve for varying the partial flows, which variation may be into equal or unequal parts, for subsequent division of the partial flows again into two or more partial flows, and the partial flows being led into the swirler via a lead-in channel each. The stepwise division of the volume flow into more and more partial flows, however, also leads to disadvantageous turbulences. Since all valves in this arrangement are continuously adjustable, disadvantageous turbulences are also generated in the partial flows due to the narrowed flow sections.